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SYSTEMS BIOLOGY, MOLECULAR BIOLOGY, AND GENE REGULATION

Physiological Roles of the β-Substituted Alanine Synthase Gene Family in Arabidopsis^1,[W],[OA]

Graduate School of Pharmaceutical Sciences, Chiba University, Chiba 263–8522, Japan (M.W., K.S.); RIKEN Plant Science Center, Yokohama 230–0045, Japan (M.K., A.O., A.F., K.S.); and Faculty of Pharmaceutical Sciences, Tokushima Bunri University, Tokushima 770–8514, Japan (M.N.)

The β-substituted alanine (Ala) synthase (Bsas) family in the large superfamily of pyridoxal 5'-phosphate-dependent enzymes comprises cysteine (Cys) synthase (CSase) [O-acetyl-serine (thiol) lyase] and β-cyano-Ala synthase (CASase) in plants. Nine genomic sequences encode putative Bsas proteins in Arabidopsis thaliana. The physiological roles of these Bsas isoforms in vivo were investigated by the characterization of T-DNA insertion mutants. Analyses of gene expression, activities of CSase and CASase, and levels of Cys and glutathione in the bsas mutants indicated that cytosolic Bsas1;1, plastidic Bsas2;1, and mitochondrial Bsas2;2 play major roles in Cys biosynthesis. Cytosolic Bsas1;1 has the most dominant contribution both in leaf and root, and mitochondrial Bsas2;2 plays a significant role in root. Mitochondrial Bsas3;1 is a genuine CASase. Nontargeted metabolome analyses of knockout mutants were carried out by a combination of gas chromatography time-of-flight mass spectrometry and capillary electrophoresis time-of-flight mass spectrometry. The level of -glutamyl-β-cyano-Ala decreased in the mutant bsas3;1, indicating the crucial role of Bsas3;1 in β-cyano-Ala metabolism in vivo.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Kazuki Saito (ksaito{at}faculty.chiba-u.jp).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.107.106831

^* Corresponding author; e-mail ksaito{at}faculty.chiba-u.jp.

Received August 3, 2007; accepted November 2, 2007; published November 16, 2007.

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